1. Field of the Invention
This invention relates generally to exhaust manifolds, and more particularly to shaping and welding pipe members of an exhaust manifold.
2. Description of the Related Art
Generally, exhaust manifolds for an internal combustion engine include a plurality of discrete pipe members that extend through a flange plate and converge into one or more exhaust pipes. Pairs of adjacent pipe members have side walls that longitudinally abut each other at their downstream ends. The side walls in each abutting pair are welded to each other in order to seal the pipes from any exhaust back flow. Welding the side walls of each pair together adds more lateral support to the pipes and ensures that the pipe members do not rub or hit each other when the engine is running or when the vehicle is moving.
FIG. 1 is an elevational cross-sectional view of a pair of abutting pipe members 10 which extend from an engine in a downstream direction toward an exhaust pipe, as part of an exhaust manifold. Downstream, each of the pair of pipe members has a side wall 12, which is depicted substantially vertical in FIG. 1. In the downstream end portion of the pair 10, the side wall of each pipe member is in confronting relationship with and abuts the other side wall of the pair. This pipe member structure is referred to as a D-shaped pipe member having a D-shaped cross-sectional configuration. Each D-shaped pipe member of the pair of pipe members 10 has a D-shaped cross-sectional configuration that is a mirror image of the other opposite D-shaped pipe member, with the illustrative mirror line being the line of confrontation with the opposing side wall. This pairing of cross-sectional configurations provides an economy of space so that each pair of pipe members 10 of the exhaust manifold can extend directly through an outlet opening 14 in the flange plate 16 into an associated one of a plurality of exhaust pipes. This arrangement eliminates a collector piece that was often required in previous practice to accept engine exhaust gases from the pipe members and convey the exhaust gas downstream to a flange plate or exhaust pipe.
The D-shaped cross-sectional configuration of the pipe member at its downstream end portion (where the pipe members converge) enables the pairs of pipe members to extend directly through the outlet openings in the flange plate into the associated exhaust pipe and eliminates additional collector pieces. However, during operation of the engine, sections of each side wall of the pair of pipe members expand in differing directions along the length of the downstream end portions of the pipe members as illustrated by the horizontal arrows 18 shown in FIG. 1, forming a zigzag pattern of stress (and resultant strain) on the respective side member 12 of each of the pair of pipe members. When the engine is turned off, the side walls of each pair of D-shaped pipe members contract as they cool, often rubbing or sliding against each other as they straighten out in returning to their original position. Such contractions often generate an objectionable "pinging" noise and also wear down the pipe members at these areas, reducing the life of the exhaust manifold. As such, there is currently a need for an exhaust manifold pipe weld assembly which eliminates or reduces these concerns.